1. Field of the Invention
The present invention relates an improvement in a processing method for high-temperature exhaust gas, and more specifically to a technical field of a processing method for high-temperature exhaust gas in which high-temperature exhaust gas discharged from a reducing furnace for producing reduced iron is controlled in temperature by a temperature control tower to enable effectively separating and recovering solid dust, and volatile and melting components contained in the high-temperature exhaust gas.
2. Description of the Related Art
As is known, the temperature control tower has a function for cooling the high-temperature exhaust gas discharged from a high-temperature gas generating source such as incinerator, a melting furnace or the like by spraying cooling water or by a wet type processing method using a scrubber in order to use it as a heat source for a boiler in the subsequent step and to obtain a temperature suitable for being processed by a bag filter.
However, flying ash or solid dust containing volatile components such as zinc, lead or the like, and melting components such as alkaline metal, oxide, chloride or the like are mixed in the high-temperature exhaust gas discharged from the incinerator or the melting furnace, and the temperature control of such a high-temperature exhaust gas containing such a flying ash or solid dust only by cooling water spray causes a problem of the adhesion of the liquefied matter of the volatile component or the solidified matter of the molten component to the inner wall of a temperature control tower. Further, the wet type processing method has a problem of being disadvantageous in respect of equipment cost such that water treatment equipment is necessary, because water-soluble components are contained in the volatile component or the melting component.
Therefore, for solving the problems noted above, various temperature control systems have been proposed. For example, there 3 a technique in which high-temperature gas is injected in a tangential direction of a circle formed by a horizontal section of a temperature control tower and obliquely downward from a purge gas blowing duct branched from an exhaust gas introducing duct to whirl the purge gas, and in which an overflow dam is provided at the upper part within a temperature control tower to flow down water over-flown from the overflow dam along the inner wall to thereby prevent the deposit from being adhered to the inner wall of the temperature control tower. There is another technique in which a plurality of high pressure liquid injection nozzles are provided on the pipe walls of a combustion exhaust gas cooling chamber (corresponding to a temperature control tower) to emit high-pressure fluid against the pipe inner walls of the combustion exhaust gas cooling chamber from these high-pressure liquid injection nozzles to thereby remove the deposited dust.
Further, as a technique for processing wastes containing iron or zinc, lead and so on which are volatile components, there is an exhaust gas processing method used when ironmaking and steelmaking wastes are processed, which merely cools exhaust gas by cooling oil, which makes exhaust gas to pass through a coke filling layer, and which makes exhaust gas to pass through a cyclone to recover dust.
In the case where the high-temperature exhaust gas is blown-in as purge gas to whirl it, the volatile and melting components contained in the high-temperature exhaust gas cannot be cooled completely, and therefore, the effect of preventing the volatile and melting components from being adhered to the inner wails of the temperature control tower is not always obtained satisfactorily. Further, the flowing down of water along the inner walls of the temperature control tower requires water treatment equipment for processing the water-soluble components. Furthermore, in the case where high-pressure fluid is emitted, this is a mere expectant treatment, not preventing the volatile and melting components themselves contained in the high-temperature exhaust gas from being adhered to the inner walls of the temperature control tower. Besides, this is a mere technique relating to cooling of the high-temperature exhaust gas, which is not for a purpose of separating and recovering solidified solid dust to effectively use recycling or the like.
Incidentally, equipment for combusting-melting processing wastes containing metal such as a furnace for directly melting industrial wastes has been recently studied. In cases of such equipment as described, since many of volatile low melting-point substances such as zinc, lead, alkaline metal such as Na and K are contained, a problem of adhesion of the low melting-point substances is more conspicuous. Further, attention has been paid to a technique in which a carbonaceous reducing agent such as coal, metal oxide such as iron ore or wastes containing metal oxide, as raw materials, at a high temperature of not less than 1000xc2x0 C. are reduced or reduced and molten to obtain reduced iron. However, since these raw materials contain a large quantity of volatile and melting components and gases at an extremely high temperature are generated, cooling of gas is hard to consistent with the prevention of adhesion, and at the present time, an effective temperature control tower is not proposed.
In the case where the exhaust gas is cooled by cooling oil, since oil is contained in the exhaust gas after temperature has been controlled, it is necessary to provide separate equipment for the post-processing of exhaust gas. In the case where the exhaust gas is allowed to pass through the coke filling layer, when solid iron oxide or volatile component such as zinc and lead are contained in the exhaust gas, these are easily adhered to the coke, and closure (blockage) occurs, thus posing a problem in that continuous operation is difficult. Further, in the case where the exhaust gas is allowed to pass through the cyclone, since cooling is not conducted, solid dust of large size can be separated but when sold iron oxide or volatile component is contained in the exhaust gas, these are easily adhered to the inside of the cyclone, and closure easily occurs, thus posing a problem in that continuous operation is difficult. All these cases attach importance to the recovery of dust, but are not provided with the cooling performance capable of sufficiently cooling the high-temperature exhaust gas. There has not been provided a processing method capable of being consistent the cooling of the high-temperature exhaust gas with separation and recovery of solid dust, every dust component.
Moreover, in prior art, even if the dust components should be recovered, they are not separated every component. Therefore, the recycle cannot be achieved of course, and the effective utilization cannot be made. Disposal was only way to do.
Furthermore, in the case where cooling is made merely by spraying cooling water as in prior art, there poses a problem in that it is necessary to increase a quantity of spraying cooling water so that it easily causes the trouble of corrosion by acid and also the volatile and melting components are excessively cooled to make large the grain size of the solidified volatile and melting component dust, and both the solid dust and the volatile and melting component dust become precipitated under the temperature control tower 2, failing to separate and recover them.
It is therefore an object of the present invention to provide a processing method for high-temperature exhaust gas for cooling high-temperature exhaust gas effectively while effectively preventing adhesion of volatile or molten components to the inner walls of a temperature control tower, solidifying the volatile or molten components to effectively separate and recover solid dust and the volatile or molten components, and enabling acceleration of recycling of the dust recovered.
Means employed by the processing method for high-temperature exhaust gas according to claim 1 or 2 of the present invention for solving the above-described problems comprises: blowing high-temperature exhaust gas discharged from a high-temperature gas generating source into a temperature control tower provided with an extended step part whose diameter is extended toward the downstream of the high-temperature exhaust gas, spraying cooling water toward a gas flow of the high-temperature exhaust gas blown, and further, injecting cooling gas along the inner walls of the temperature control tower from cooling gas injection means provided on the extended step part, controlling the temperature so that the high-temperature exhaust gas blown assumes an adequate temperature, discharging and recovering solid dust separated from the high-temperature exhaust gas by the temperature control outside the temperature control tower, and recovering volatile or molten dust contained in the exhaust gas after having been controlled in temperature discharged from the temperature control tower by a bag filter.
Means employed by the processing method for high-temperature exhaust gas according to claim 3 of the present invention depending on claim 1 lies in that cooling gas is injected, from the cooling gas injection means, obliquely downstream so as to be a whirling gas flow along the inner walls of the temperature control tower.
Means employed by the processing method for high-temperature exhaust gas according to claim 4 of the present invention depending on either claim 1 or 3 lies in that cooling gas is injected, from cooling gas injection means provided on the upstream side of the extended sit, in a quantity more than that of cooling gas injection means provided on the downstream side.
Means employed by the processing method for high-temperature exhaust gas according to claim 5 of the present invention depending on any of claims 1 to 4 lies in that unrecovered solid dust contained in the exhaust gas after having been controlled in temperature discharged from the temperature control tower is recovered by a cyclone before the volatile or molten component dust is recovered by the bag filter.
Means employed by the processing method for high-temperature exhaust gas according to claim 6 of the present invention depending on any of claims 1 to 4 lies in that unrecovered solid dust contained in the exhaust gas after having been controlled in temperature discharged from the temperature control tower is recovered by a high-temperature bag filter before the volatile or molten component dust is recovered by the bag filter.
Means employed by the processing method for high-temperature exhaust gas according to claim 7 of the present invention depending on any of claims 1 to 6 lies in that the high-temperature gas generating source is a reducing furnace which reduces, or reduces and melts at a high temperature the raw material containing a carbonaceous reducing agent such as coal and metal oxide contained substances such as iron ore to produce reduced metal.